There are many sensors for measuring properties of fluids, and they vary widely in utility, sensitivity, ruggedness and reliability. It is a desirable objective to provide a rugged, simple and reliable sensor to respond to properties of fluids which are related to the opposition by the fluid to its own physical displacement. Examples of applications for such a sensor are determining the quality of a fluid, i.e., whether the fluid is all liquid, all gas, all vapor, or some mixture of them. Such information can, in turn, be used for information alone, or to control a system to restore the qualilty to some desired value. An example of a system utilizing this information is a control for the level of oil supply in an internal combustion engine. There are, of course, other applications for sensors which utilize different displacement resisting properties, for example viscosity, to determine some monitored condition of a fluid, for example the degree of dilution of oil by gasoline.
By sensing the opposition of a fluid to its own displacement, information can both be obtained and can be put to use to control systems which utilize the fluid for some other purpose. To this end, the sensor can also be used as a pump to cause the fluid to flow in a system for an advantageous purpose. One example of such an arrangement is the maintenance of a correct oil level in an internal combustion engine as discussed above. An additional advantage which can be secured is the incorporation of external oil reservoirs in the engine oil system which form part of the actively-used lubricant, rather than merely a static reserve. This extends the period between oil changes and the addition of oil, and enlarges the protection of oil systems from excessive dilution by engine fuel. These are important advantages when the engine is in a remote location, or one which is difficult to reach. Improving the reliability of an engine, and decreasing the frequency of routine service visits, can make appreciable cost savings possible.
There are many other uses to which the type of information derived by a sensor according to this invention can be employed for control purposes. It must be said that the applications for sensors according to this invention can be fulfilled by other types of sensors, which may or may not use the same physical property. However, many of the most useful applications of this sensor are in circumstances where ruggedness, simplicity, compactness, and reliablity are at a premium, and the sensor of this invention greatly excels many of the conventional sensors available as an alternate.
The range of possible fluid substances with which this invention may deal is limited generally to those which can be pumped or otherwise caused to flow in a fluid path or duct. Within this limitation it may deal with a broad range of possible fluids, which may consist of or contain gases or vapors, liquids, emulsions, mists and even suspended or entrained solids. Among fluids of the same composition there maybe variations in physical conditions such as temperature, pressure, viscosity, or vapor pressure, which it may be useful to identify. Variations in the state or quality of the fluid system which may affect opposition to fluid displacement may include differences in head or state of flow, or the presence or absence of a fluid at a particular point in the fluid system.
A substantial application for this invention is one wherein the sensor senses whether there is a liquid or a gas at the sensed location. In an oil lubrication system, for example, the sensing of gas can indicate that the oil level is too low. The sensing of liquid may indicate a sufficient or too high an oil level. Whatever the situation, the intended discrimination is between the presence of gas or of liquid.
However, the situation can become complicated at extreme conditions of operation, such as when an oil system is extremely cold. To provide optimum sensing, the system should be relieved from sensitivity to extremes of variables as much as possible.